This invention relates to a vision-based arc welding control system and method of closed-loop weld process control, and to more effective weld puddle geometry discriminants to provide quality welds with full penetration for thin sheet metal parts.
An optical viewing system integrated into a TIG (tungsten inert gas) welding torch provides direct images of the weld pool and joint as viewed axially along the torch electrode. The primary components of the vision system are a laser pattern generator, the through-torch sensor, a solid state imager, and a distributed microprocessor for real-time image analysis. A first coherent fiber optic bundle transmits laser spots to floodlight the weld puddle and a laser pattern, such as two parallel stripes, projected close to the weld puddle to determine joint location and width. A second coherent fiber optic bundle transmits the image of the weld puddle, laser stripes and surrounding weld region to the imager. The vision system analyzes the weld puddle and determines geometry parameters such as puddle dimensions and position of the puddle relative to the joint. Arc welding torches with integrated optics and other aspects of the robotic welding system are described in the assignee's patents and copending applications.
It is desirable to monitor and control the robotic welding process in real time to insure high quality welds. In many applications, variations in local metal thickness, joint width, heat sinking, and grounding geometry may lead to unacceptable errors in weld bead width penetration, and resultant seam geometry. By using vision sensors such as the foregoing that can monitor the welding process in real time, weld quality can be maintained through closed-loop process control.
Vision systems used for automating the TIG welding process have been based solely on measuring the weld puddle width in order to provide a uniform quality weld with full pentration. One of those using puddle width to control the process, developed at the Center for Welding Research, Ohio State University, is described in "A Vision Based System for Arc Weld Pool Size Control", R. W. Richardson et al, Measurement and Control for Batch Manufacturing, ed. by D.E. Hardt, ASME, November 1982, pp. 65-75. There are many disturbances in the welding process, such as variations in filler wire feed rate, which can cause a change in the weld puddle width. If the welding process parameters such as velocity and weld current are changed to control the width this does not necessarily result in the desired weld bead quality.